The purpose of this study is to determine the relationship between several indices of systemic stores of iron with the surrogate gold standard, serum ferritin, for measurement of iron status, and erythropoietin sensitivity. This study will also assess the sensitivity and specificity of the response of these various measures of iron stores to an intravenous dose of iron dextran. Finally, the relationship between administered iron dose, the multiple iron indices, and erythropoietin sensitivity will be evaluated.